Approximate Duals of $g$frames and Fusion Frames in Hilbert $C^ast$modules

In this paper, we study approximate duals of $g$frames and fusion frames in Hilbert $C^ast$modules. We get some relations between approximate duals of $g$frames and biorthogonal Bessel sequences, and using these relations, some results for approximate duals of modular Riesz bases and fusion frames are obtained. Moreover, we generalize the concept of $Q$approximate duality of $g$frames and fusion frames to Hilbert $C^ast$modules, where $Q$ is an adjointable operator, and obtain some properties of this kind of approximate duals.